The present disclosure relates to a fixing device which fixes a toner image on a sheet and an image forming apparatus including the fixing device.
An electrophotographic type image forming apparatus is provided with a fixing device including a pressuring roller which comes into pressure contact with a fixing roller which is to be heated. The fixing device includes a pressure changing part which changes pressure at a fixing nip formed between the pressuring roller and the fixing roller. The pressure changing part changes the pressure at the fixing nip by turning a fixing roller supporting frame around an axis.
The fixing device further includes a rotation detecting part which detects rotation of the pressuring roller via a plurality of gears. The rotation detecting part detects rotation of the fixing roller by detecting the rotation of the pressuring roller. Thereby, the fixing roller can be prevented from being heated locally in a state where the rotation of the fixing roller is stopped.
A driving force transmitting device which transmits driving force to the fixing roller has been known although not a mechanism which transmits rotation force from the pressuring roller to the rotation detecting device. An example of the driving force transmitting device has a driven gear fixed to the fixing roller and a fixing roller driving gear which is rotatably supported by a side frame to which a fixing unit (the fixing device) is fixedly attached. In the driving force transmitting device, a rotating shaft (a pin) of the fixing roller driving gear is engaged with an engagement part formed in the fixing unit. By engaging the pin with the engagement part, the fixing roller driving gear and the driven gear are engaged with each other at a predetermined position.